Studies at the basic and clinical level continue in several heritable bone disorders. Molecular genetic studies on the structure of the transcription unit of alpha 2 Type I collagen mRNA was completed. We demonstrated that in both dermal fibroblasts and osteoblasts identical splicing patterns and promotor usage occur in man and chick, suggesting alternative mechanisms must operate in tissue-specific regulation in different connective tissues. Studies began on the cloning of bone-specific human alkaline phosphatase, with the protein purified to homogeneity from human liver and a partial protein sequence data determined. Studies of the molecular defect in osteogenesis imperfecta continue with preliminary development of several new methods of delineating the collagen-specific subsets underway. Clinical studies in O.I. on the relationship of IGF I and II to growth failure show some promising correlations. Bracing as a treatment modality in childhood O.I. patients was continued. In the study of fibrodysplasia ossificans progressiva, treatment with 13-cis retinoic acid enters its 3rd year, with continued promise. The existence of a polar prostanoid in the plasma of patients with FOP has been confirmed and its identity at present is being determined. A new disorder of heteroptic ossification, limited dermal ossification, was described this past year.